Mats of an elastic material and provided on their undersides with projections can be used as a support layer for a bed of ballast in railway or highway applications.
These mats can be provided with a layer on their upper side, which comprises a material different from that of the rest of the mat and serving to limit ballast movement. They serve the ballast bed and the track by providing an elastic, cushioning layer on the ground, on the tunnel and trough walls according to the application, in order to effect sound damping or attenuation of sound conduction.
In known mats of the foregoing kind the upper side of the mat can be provided with a layer of a plastically deformable material as taught in German Patent document DE-GM No. 80 13 779, for example, a bituminous layer.
The ballast bed stone can penetrate to a certain extent into this layer, so that an extended antiskid or antislide layer is the result. A disadvantage of this kind of mat, however, is that the ballast, i.e. crushed stone, gravel, metallic particles, or the like, with sharp edges penetrates through the mat in a comparatively short time, whereby the mats are destroyed, so that finally all that is left is a granular bed or granulated remnant of the mat. Such a granulated remnant provides little or no acoustic damping or insulation.
Another known form of mat has a sheet-metal layer on its upper side as taught in German Patent document DE-OS No. 31 21 946 (see U.S. Pat. No. 4,500,037), which prevents the penetration of the ballast of crushed stone, metallic particles or the like into the mat. These mats provide a particularly high degree of acoustic damping and insulation; they are however only limitedly bendable or flexible, so that they can only extend over very short distances at the place where they are to be installed and a large number must be assembled at high labor cost.